Add contrib/credentials/netrc with GPG support

This credential helper supports multiple files, returning the first one
that matches.  It checks file permissions and owner.  For *.gpg files,
it will run GPG to decrypt the file.

Signed-off-by: Ted Zlatanov <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: tzz

contrib/credential/netrc/Makefile

@@ -0,0 +1,5 @@
+test:
+	./test.pl
+
+testverbose:
+	./test.pl -d -v